Evaluation of surface deflection in automobile exterior panel by curvature based method

Surface deflections in exterior panel have a great effect on the external appearance of automobiles. Usually, they are occurred on large flat panels containing sudden shape changes and shows very small amplitude. Traditional methods for detecting surface deflections on stamped automobile panels are scratching the surface with a wheatstone with oil, rubbing the surface with technician's fingers, or reflecting light on the surface. All of these methods rely on a technician's sense. In this study, a curvature based method was proposed to detect and quantify the surface deflection. The measure of surface deflection was defined as the variation of curvature difference between tool and blank. The degree of surface deflection can be predicted by the correlation between the proposed measure and visual inspection. Today's simulation code has enough accuracy to predict surface deflection by using the proposed method. The appropriate simulation method to find the surface deflections accurately were studied. As a verification example, a shallow rectangular drawing with rectangular embossing was studied. The corresponding experiment was carried out. The simulation and experiment were compared and investigated to prove the effectiveness of the proposed method and the effectiveness of prediction.